FI80717B - Process for producing pellets consisting of carbon or a carbon-containing material - Google Patents

Description

1 80717

The present invention relates to a process for preparing pellets from carbon or carbonaceous material.

Despite extensive efforts, it has not been possible so far to develop a technically simple and inexpensive method for removing or reducing NOz in the flue gases of coal-fired plants. In principle, two types of methods are used to remove or reduce NOx and other undesirable components from the flue gases, on the one hand by methods which influence the combustion process itself, e.g. by using fuel additives, and on the other hand by removing unwanted components from the flue gases themselves.

In particular, the present invention relates to the reduction of NO 2 using a method of the former type.

For example, it is known from GB Patent Specification 2,046,781 that calcium compounds are added to carbonaceous solid fuels to reduce unwanted components of flue gases, e.g., sulfur compounds.

U.S. Patent No. 1,990,948 states that ferric chloride and ferrous sulfate can be used in the manufacture of solid fuel compacts.

However, the presence of large amounts of chlorine and sulphate in the feeds of combustion processes is not desirable, as corrosion of metal surfaces can occur and flue gases then contain potentially harmful substances.

U.S. Patent No. 3,323,901 discloses the manufacture of extrudates containing iron ore, coal and Portland cement. These extrudates are intended to be used as fuel for the iron smelting process and therefore may contain a significant amount, e.g. 60 to 35% by weight of iron ore. Portland cement is used as a binder.

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There are no indications that the presence of iron would have any beneficial effect on the amount of undesirable components in the resulting fuel gases. A person skilled in the art, who reads the description of U.S. Patent 3,233,901 5, will probably not undertake to make solid fuels that contain less coal, calcium compounds, and iron compounds than would be the case in the feed of its smelting process.

U.S. Patent No. 2,844,112 discloses a method 10 for preventing the formation of slag in boilers heated by waste oil by adding various substances to the fuel that contain calcium and iron compounds. However, solid carbonaceous materials such as coal behave differently from waste oil fuels in terms of slag formation. Those in control of the industry are unlikely to add to the coal substances used in waste fuels to prevent the formation of slag to prevent the formation of slag.

We have now found that by using a certain combination of additives, a solid fuel can be obtained which has a reduced tendency to form when burning NOX.

The invention relates to a process for the preparation of pellets from finely divided carbon or carbonaceous materials, a first thermosetting binder which is water-soluble or water-swellable and a second binder based on aqueous emulsions of heavy hydrocarbons, with up to 10% by weight of carbon added to the carbon ( daf) calcium oxide 30 or an equivalent amount of calcium hydroxide, calcium carbonate and / or substances containing these compounds or forming them under combustion conditions, and the mixture is agglomerated in a pelletizer with the addition of a binder, then the green pellets thus obtained are thermally dried and thermally dried. 3,80717, a binder concentration gradient is obtained by the controlled addition of the first and separately the second binder during pelletization, so that the concentration of the first binder in the green pellets and the concentration of the second binder decreases from the outside to the inside, and 0.1 to 5%, calculated on carbon (waf), of iron, which is iron oxide, iron carbonate, and / or elemental iron and / or substantially halogen-free, sulphate-free, is added to the pelletizing mass. , in the form of iron - rich minerals or technical by - products.

Examples of compounds which form calcium oxide under the conditions of the furnace are calcium barrels, e.g. CaO, Ca (OH) 2, CaCO3 or materials containing significant amounts of these compounds free or bound, such as dolomite CaCO3 · MgCO3.

The reference to the equivalent amount of other calcium compounds is to be understood as measuring compound 20 in an amount equal to the amount of calcium present in the calcium oxide.

Iron oxide, iron carbonate and / or elemental iron can be fed in a sufficiently pure form. Alternatively, they may be fed as iron-rich minerals or as industrial wastes of iron oxide or carbonate, e.g. basic iron hydroxide, ferrous metallurgical wastes, e.g. iron oxide dust, blast furnace slurry, LD slurry, rolled coal, iron-rich means 30 here an iron content of at least 20, in particular 30 to 60% by weight.

The solid carbonaceous fuel may be hard coal in the form of coal powder or coal dust, coal coke, petroleum coke or lignite. The fuel 35 can be used in powder form when used in combustion plants for pulverized fuels, but use as agglomerates, especially pellets, is also preferred. Pellets with particularly advantageous properties to which the additives of the invention can be applied are known from DE-A-3 321 683 (corresponding to EP-A-97 486).

The additives of the invention are preferably finely divided or well dispersed in the fuels; a particularly advantageous distribution is observed when the pellets are prepared according to DE application 3 321 683, especially in the presence of sugar-containing compounds.

The aforementioned interaction of the individual components of the additives of the invention is determined on the basis of tests, the description of which will follow later.

The structure of the incinerator is shown in the diagram shown in Figure 1 and the structure of the incinerator in Figure 2.

Combustion air is supplied to the laboratory furnace 1 via flow meters 2 and 3. Gas to ignite the furnace can be passed along line 4. Locations 5 have Pt-Re-thermopa-20 rit. The furnace gases are led into the chimney (not shown) * 'along line 6. A gas flow is separated into line 7 and immediately fed to a coarse filter 8, a fine filter; : through the condenser 10 and pump 11 of the radiator 9 to the gas analyzer 12 and then to the chimney (not shown).

The structure of the incinerator will now be described in more detail with the aid of Figure 2.

The cylindrical kiln is made of high temperature resistant steel and has three parts 13, 14 and 15: 30 blowing area with high temperature resistant steel grille as base and bottom air (16) inlet to the hole bottom (17) below it, cylindrical middle part made of stone and an upper air supply (18) having an annular structure, the upper part 35 having a void space at the top.

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The inner diameter of the inner part of the cylindrical furnace is 150 mm and the total free height is 600 mm, and the cylindrical part tapers conically so that its inner diameter in the uppermost part is 50 mm. The sheath is similarly insulated from high temperature steel on the outer surface and insulated on the inner surface as follows: insulating ceramic layer, insulating cast layer, refractory insulating material made by tightly packing the granular material.

The Pt-Re thermocouples are connected to the central part where the coal enters, and one thermocouple is also connected to the empty space at the top.

Flue gases leave the top of the furnace and go into the smoke-15 chimney; part of the flue gas flow is sucked in for analysis. This partial flow is filtered twice to remove tar and dust and cooled to 2 ° C to reduce the partial pressure of water. The flue gas thus treated is then continuously analyzed for the gaseous components NOx, SO2, CO, CO2 and O2.

After the analyzer for flue gas components has been calibrated, the upper part of the incinerator is raised initially. 1 kg of lignite (coal pellets with a mean diameter of 10 mm) is fed in so that the height of the carbon layer becomes about 10 cm. The overlapping layers of the furnace are then closed and four thermocouples are installed. The coal is ignited by means of a gas burner through the bottom of the hole in the bottom of the furnace. Next, air (8-12 Nm3 / hour) is blown into the coal, so that the amount of upper air is about 70% and the amount of lower air is about 30%.

Depending on the type of coal, the combustion temperature rises to about 1500 eC during combustion.

After a test period of about 30 to 50 minutes, depending on the flow of air and the type of carbon, combustion is practically complete, as can be seen from the analysis (O 2, CO 2) and the temperature curve.

The kiln, viewed in terms of the temperature curve and the composition of the exhaust gas, simulates the combustion process 5 as a function of time, which simulation is obtained with a conventional industrial chain grate as a function of grate length.

The test molds were made of Middelburg coal. The following substances were used as binders in the manufacture of extrudates: 2-8% by weight of water-soluble or water-swellable organic binders for basic strength, e.g. molasses types and starch derivatives (in a separate example described below: 8% by weight of sugar cane molasses (45% by weight of water) carbon (daf).

15 to 3% by weight of a weather-resistant and water-repellent surface protection agent, e.g. bitumen and other processing residues (Visbreaker), in the form of an emulsion (in the following separate example: 2% by weight of bitumen emulsion (40% by weight of water) based on carbon (daf)).

20 5% by weight of slaked lime (about 96% Ca (OH) 2), which met the requirements of the DIN standard *: "for white fine lime" (= Weissfeinkalk), and / or 3% by weight of iron oxide dust (about 64% by weight) were added as additives. iron); % by weight again for carbon (daf).

The preparation of the pellets was carried out according to the embodiment of DE application publication 3 321 683 (EP 97 468).

Based on the results of the continuously recording gas analyzer *, the N0X emission was determined. Comparing the total NOx emissions obtained for extruders without *: 30 additives, for extrudates with individual additive components and for extrudates with a combination of additives, it is observed that the N0X values in the flue gas decrease, as can be seen from the following table; the combustion conditions (about 12 Nm 3 / hour) were identical and the results are very reproducible. NOx is expressed in milligrams of 7,80717 NOx calculated as NO2 per kilogram of coal (daf).

Additive NO? (Mg / kg) NO 2 reduction (%) 5 No additives 1530.6 0 5% slaked lime 1327.6 10 3% iron oxide 10 dust 1338.8 12.5 5% slaked lime and 15 3% iron oxide dust 824.9 46

The results show the combined effect of Ca (OH) 2 and Fe2O3 on NOx emissions.

Claims (1)

A process for preparing pellets from finely divided carbon or carbonaceous materials, a first thermosetting binder which is water-soluble or water-swellable, and a second binder based on aqueous emulsions of heavy hydrocarbons, up to 10% by weight of carbon being added to the carbon. (daf) calcium oxide or an equivalent amount of calcium hydroxide, calcium carbonate and / or substances containing or forming these compounds under combustion conditions, and the mixture is agglomerated in a pelletizer with the addition of a binder, the green pellets thus obtained are thermally dried, then thermally dried and cured binder concentration gradient by the controlled addition of the first and separately the second binder during pelletization, so that the concentration of the first binder in the green pellets ä decreases from the inside out to 20 and the concentration of the second binder decreases from the outside inwards, characterized in that 0.1 to 5% by weight, based on carbon (waf), of iron, iron oxide, iron carbonate, and / or elemental iron and / or or in the form of substantially halogen-free, sulfate-free, iron-rich minerals or technical by-products. 9 80717 For use in the manufacture of pellets from a finely divided material, in which case the color of the pellets is separated from the pellets by means of a pellet in the form of an emulsion , varvid tilti kolet tillsätts högst 10 vikt-%, beräknat pä mängden koi (daf), calcium oxide or the equivalent of calcium hydroxide, 10 calcium carbonate and / or amine, which is a mixture of the same or more than one of the fineness of the image 1 en pellet-ringmaskln under tlllsats av bindemedel, de säledes er-hällna Gröna pelletarna prickas termiskt och härdas däref-15 ter thermiskt, varvid en concentrationsgradient hos binde-medlet erhälles i de Gröna pelletarna genom controller tillats av det for the purpose of pelleting, the concentration of pelleting in the field of pelleting is in-20 inches and concentrations of detergent binders in which the pelleting mass is reduced to a maximum of 0.1 - 5% by weight, in the form of a mole (waf), in the form of an oxide, carbonate or other elements och / eller i form av väsentligen ha-25 logenfria, sulfatfria, rikligt järnhaltiga Mineral eller tehniska biprodukter.